The present invention relates to processing data in a satellite positioning system (SPS), such as the Global Positioning System (GPS), and more particularly relates to methods and apparatuses for distributing location-based information that may be associated with a SPS.
SPS receivers, such as those which operate in GPS or other satellite positioning systems, normally determine their position by computing relative times of arrival of signals transmitted simultaneously from a multiplicity of satellites, such as GPS, NAVSTAR, or other satellites. These satellites typically transmit, as part of their satellite data message, timing and satellite positioning data, which is sometimes referred to as xe2x80x9cephemerisxe2x80x9d data. The term xe2x80x9cephemerisxe2x80x9d or xe2x80x9csatellite ephemerisxe2x80x9d is generally used to mean a representation, such as an equation, which specifies the positions of satellites (or a satellite) over a period of time or time of day. In addition, the satellites may transmit data to indicate a reference time, such as time-of-week (TOW) information, that allows a receiver to determine unambiguously local time.
Typically, an SPS receiver computes one or more xe2x80x9cpseudorangexe2x80x9d measurements, each of which represents the range between the receiver and a satellite vehicle (SV). The term xe2x80x9cpseudorangexe2x80x9d is generally used to point out that the range measurement may include error due to one or more factors, including, for example, the error between time as indicated by the clock of the SPS receiver and a reference time, such as the reference time associated with the more accurate atomic clock of the satellites. Thus, the SPS receiver typically uses the pseudoranges, along with timing and ephemeris data provided in the satellite signal to determine a more accurate set of navigational data, such as position, time, and/or range. Collecting satellite data, such as ephemeris data, provided in a satellite message requires a relatively strong received signal level in order to achieve low error rates, and may also require a relatively substantial processing time in some systems.
Most GPS receivers utilize correlation methods to compute pseudoranges. These correlation methods are performed in real time, often with hardware correlators. GPS signals contain high rate repetitive signals called pseudorandom (PN) sequences. The codes available for civilian applications are called C/A codes, and have a binary phase-reversal rate, or xe2x80x9cchippingxe2x80x9d rate, of 1.023 MHz and a repetition period of 1023 chips for a code period of 1 msec. The code sequences belong to a family known as Gold codes. Each GPS satellite broadcasts a signal with a unique Gold code. Alternative methods, as exemplified in U.S. Pat. No. 5,663,734, operate on snapshots of data and utilize fast convolution methods to compute the pseudoranges.
All of the above systems may benefit by communicating with the resources of a remote site, or xe2x80x9cserverxe2x80x9d utilizing a wireless communications system, such as a cellular telephone system. Such a server may provide assistance data to the mobile GPS receivers to enhance their performance, receive data from the GPS receivers and perform further processing on such data to complete or refine a position calculation, etc. In addition, the remote site may include or be connected to various display and application resources, such as a dispatching system to send emergency or repair resources to the user of the GPS mobile, or to provide route guidance or other concierge services.
Thus, the above server may provide two functions: (1) Location Server functions, which provide assistance to the mobile GPS receivers to enhance their performance, and (2) Application Server functions, which display the location of the mobile GPS receiver and provide auxiliary services, such as roadside assistance.
A paper was provided by Raab in 1977 on splitting the functionality of GPS processing between mobile GPS receivers and a remote basestation. See Raab, et al., xe2x80x9cAn Application of the Global Positioning System to Search and Rescue and Remote Tracking,xe2x80x9d Navigation, Vol. 24, No. 3, Fall 1977, pp. 216-227. In one method of Raab""s paper the remote GPS receiver computes the times of arrival of the satellite signals at the remote GPS receiver (so-called xe2x80x9cpseudorangesxe2x80x9d) and transmits these times-of-arrival to a central site via a data relay where the final position calculation of the mobile is computed. Raab also mentions providing assistance information including approximate time and position to the remote unit. Raab also discusses so-called xe2x80x9cretransmission methodsxe2x80x9d in which the raw GPS signal is relayed directly to the remote basestation.
Other patents, such as U.S. Pat. Nos. 4,622,557, 5,119,102, 5,379,224, and 5,420,592 discuss variations of the retransmission method. U.S. Pat. No. 4,622,557 utilizes an analog retransmission method whereas U.S. Pat. No. 5,119,102, 5,379,224, and 5,420,592 utilize digital means to store and then forward a digitized record of the sampled GPS signal. These patents describe communications between one or more mobile units and a single basestation which may incorporate functions of GPS calculation as well as ancillary functions described above.
The U.S. Pat. No. 4,445,118 by Taylor discusses transmission of aiding data, such as GPS satellites in view from a basestation to remote units via a communication link. In addition, in one variation, a tracking application for trucks, Taylor describes a system in which pseudorange data is sent from the trucks to the remote basestation which computes the final position. Variations on this pseudorange transfer method include U.S. Pat. No. 5,202,829 and 5,225,842. Again, this prior art envisioned a single basestation containing GPS aiding functions as well as display and other ancillary functions.
FIG. 1 shows a block diagram of the prior art which utilizes a basestation to supplement GPS signal processing. Mobile units 12a, 12b, 12c, and 12d in this example contain a combination of a GPS receiver and a wireless modem. Attached to the GPS unit are GPS antennas 10a, 10b, 10c, and 10d for receiving GPS signals from GPS satellites (not shown for simplicity) and antennas 11a, 11b, 11c, and 11d for communication to and from a basestation 20 which includes a basestation antenna 17. In some implementations, this communication may be in one direction only.
Basestation 9 contains a signal processing unit 15 which may provide aid to the mobile GPS units to help them obtain positioning information and/or it may complete or refine the position calculations of these units based upon data transmitted to it from these units, together with auxiliary data which it may gather with its own GPS antenna 18. The signal processing unit 15 may contain its own GPS receiver and GPS antenna in order to determine its own position and provide differential corrections to the data transmitted to it from the mobile GPS units. Basestation 9 also includes a display 14 and computer equipment which is coupled to the signal processing unit 15 by a connection 16 and which allows an operator to visually track the position of the mobiles and provide manual and semiautomatic commands to these units via the aforementioned communications links. In some cases, unit 14 together with signal processing unit 15 is termed a xe2x80x9cworkstation.xe2x80x9d
Although FIG. 1 shows a wireless link from each mobile GPS unit to the basestation, this link may actually be a wireless link to a modem, such as one at a cell site followed by a wired or other link to the basestation as shown in FIG. 1. In some implementations, the basestation 9 may actually represent a number of basestations in a reference network.
Unfortunately, in distributed systems, such as the one shown in FIG. 1, the geographical area in which a mobile unit may operate in conjunction with the basestation(s) is generally limited, for example, by the range and distribution of cellular or other communication system transceivers. As such, a mobile GPS unit may not be able to communicate effectively outside of the range provided by the basestation(s), and/or may experience delays in attempting such communication.
Therefore, what is need is an improved method and system for distribution of satellite signal-related and/or location-specific information.
The present invention provides methods and apparatuses for distributing location-based information (i.e., information specific to a client""s location or a location of interest to the client) to a client, which may be a mobile SPS receiver, via the Internet and in particular, the World-Wide Web. In one embodiment, the client provides information associated with its location and/or a location of interest to a Web server. For example, such information may include pseudorange measurements, portions of one or more received satellite messages, user-input data of known or estimated location, etc. The Web server, based on the information, provides via the Internet information relating to the client""s location or location of interest to the client.